In accordance with the work of Desai and colleagues [13], who analysed two cell lines and showed abundant expression of ISG15 in the breast cancer cell line ZR-75-1 but not in the BT474 cell line, we also found upregulation of ISG15 mRNA in several additional breast cancer cell lines analysed (that is, BT20, MDA-MB468, MDA-MB231, T47D and MCF7) when compared with the benign mammary cell lines HMEC and MCF12A. The gene discussed is ISG15; the disease is breast cancer.